docs: fix link to installation page

[gep13]

NOTE: The Testing link:

https://git-proxy.finos.org/docs/development/testing

also goes to a 404, but I couldn't find another link that I thought matched the inteded destination.

I was going to create an issue, but I didn't think that this would be needed for such a small change.

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• ✅ login: gep13 / name: Gary Ewan Park (4b47144)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.66%. Comparing base (e788ab7) to head (4b47144).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1491   +/-   ##
=======================================
  Coverage   89.66%   89.66%           
=======================================
  Files          68       68           
  Lines        4869     4869           
  Branches      888      888           
=======================================
  Hits         4366     4366           
  Misses        485      485           
  Partials       18       18           

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[jescalada]

@gep13 Thanks for the contribution! 🚀

Good catch, the actual testing documentation is in CONTRIBUTING.md. I'll add the testing guide to #1487 so we can go ahead and merge this.